The structures, hydrolytic and redox stabilities of recently discovered polytungstate and polymolydate complexes of organometal, organometalloid and organophosphorus compounds, will be determined by X-ray diffraction, miltunuclear NMR spectroscopy, electrochemistry and ESR spectroscopy. The potential of such complexes as electron dense imaging agents is to be explored by NMR and electron spin microscope studies of the binding of polymetalate derivatives to phospholipid vesicles.